Cordierite ceramic honeycombs are widely used as catalyst supports in catalytic converters for the removal of carbon monoxide, nitrogen oxides and unburned hydrocarbons from gasoline engine exhaust gases, and for the trapping of particulates present in diesel engine exhaust gases. A key factor influencing the thermal durability of cordierite substrates or filters to be used in harsh engine exhaust environments is the coefficient of thermal expansion (CTE) of the material. Under extreme temperature cycling conditions such as commonly encountered in engine exhaust systems during use, the substrate is subjected to high thermal stresses induced by thermal gradients.